What's behind dramatically cooler temperatures this week?

Temps in Indy will struggle to top 70 degrees

INDIANAPOLIS - Indianapolis is typically sweltering in mid-July, but a dramatic swing in the other direction is in store this week.

A cold front sweeping through Indiana on Monday will usher in temperatures well below average for this time of year.

Get Full Forecast

Temperatures on Tuesday in Indianapolis will struggle to top 70 degrees. That's pretty uncommon in July.

"That is not normal for us," said StormTeam 6 meteorologist Ashley Brown. "We are well below the seasonal average."

The average high temperature this time of year is 85 degrees. Tuesday's projected high temperature in Indianapolis is 72, with highs climbing slowly from that point the rest of the week.

Considering skies will be mostly sunny through the week, it will feel much more like fall than summer.

"It will be a great stretch of weather," said StormTeam 6 meteorologist Todd Klaassen. "Humidity levels will be low."

A high of 72 is more typical for late September. That's the average high for the Sept. 28-30 stretch.

To go with much cooler than normal highs, nighttime low temperatures will be well below normal, too, in the 50s.

"A few 40s will be possible, especially Wednesday morning," Klaassen said.

Indianapolis has seen some extremes in July weather recently, with July 2012 being the hottest on record and July 2009 the second-coldest since records began.

The coldest high temperature ever in Indianapolis in July was 64 degrees on July 13, 1990. The coldest low temperature was 46, hit in both 1944 and 1947.

What's Causing This Chilly Stretch?

The National Weather Service office in Chicago created a stir last week when it described the upcoming cool weather as another appearance of the polar vortex.

The root cause of the below-normal temperatures across the Midwest began on the other side of the world with Typhoon Neoguri.

The strong storm altered the path of the North Pacific jet stream, allowing polar air to spill out of Canada and into the Midwest, said Jeff Masters, of Weather Underground.

Unlike the polar vortex, the air coming into the U.S. is not directly arctic, but is from western Canada.

Indianapolis is not alone in this relatively cool stretch of weather. Chicago may not get above 70 degrees for a couple of days.

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